Thermoplastic resins, such as polystyrene, are shaped to form useful articles such as spoons, cups and other various containers. After their use, these materials have often been discarded. These articles become waste which are primarily either burnt or buried. Either burning or burying these articles causes environmental pollution. A process which recovers the thermoplastic resin in a useable form from these articles is highly desirable. By regenerating the thermoplastic resin and using this resin to form new articles, the accumulation of these articles in the environment is greatly reduced.
For recovered thermoplastic resins to be useful in general application, these thermoplastic resins must not be adversely affected by the recycling process. Any great reductions in molecular weight or fractional distribution of thermoplastic resin may render thermoplastic resin unable to form useful commercial products.
U.S. Pat. No. 3,857,799 issued to Ooba et al. relates to a process for regeneration of plastics. Plastics are regenerated by mixing the plastic with an ether-type polyester and at least one member selected from the group consisting of a homopolymer of vinylacetate, and ethylene-vinylacetate copolymer or tachypolyolefin. If necessary, a foaming agent may be added to the mixture. The mixture is then molded into a shape. The ether-type polyester is prepared by adding polyethyleneterephthalate to glycols. The polyether-type polyester is a polyethyleneterephthalate.
U.S. Pat. No. 4,031,039 issued to Mizumoto et al. relates to a method for treating waste high-polymer mixtures. This process involves fractionating the mixture by taking advantage of dissimilar solubilities of the polymers in different organic solvents characterized in that the mixture is brought into contact with o-xylene, p-xylene or m-xylene. The solvents are used singularly or in combination at a temperature within a certain range to dissolve and fractionate the mixture. The mixture consists essentially of five groups of five polymers; olefinic, polystyrenic, polyvinyl-chloride, thermosetting and natural high-polymers. The polystyrenic and polyolefinic high-polymers are removed with the xylene solvents. The remaining polymers are fractionated by using at least one solvent selected from tetrahydrofuran, cyclohexanone, dioxane, and methylethylketone.
U.S. Pat. No. 4,164,484 issued to Tokuda et al. relates to a process for recovering polyolefin and polystyrene materials. This process involves dissolving a mixture of plastics containing polyolefin-type plastics in a hydrocarbon solvent, preferably a xylene type, at a temperature not lower than 60.degree. C. The process involves vacuum-evaporating the solvent of the solution to cause precipitation of the dissolved polyolefin-type plastics and separating and recovering the major portion of the precipitate. The solution of concentrated liquor containing the precipitate and the essentially precipitate free upper phase solution are separated. The liquor is recycled and the solvent is removed from the upper phase.
U.S. Pat. No. 4,196,105 issued to Kubat relates to a process of recovery of polystyrene using liquid sulfur dioxide. This process involves contacting the polystyrene-containing starting material with liquid sulfur dioxide, thus dissolving polystyrene and the resulting polystyrene-sulfur dioxide system forms two layers. The upper layer contains low and high molecular fractions of polystyrene and the lower layer contains liquid sulfur dioxide which is generally free of polystyrene. This patent also teaches that low molecular weight portions of polystyrene can be removed from the upper phase by repeated extraction with pure sulfur dioxide.
U.S. Pat. No. 4,517,312 issued to Kumasaka et al. relates to a process for regenerating resin. The process involves regenerating a resin by dissolving the resin in an organic solvent, such as methylene chloride, trichloroethylene, or carbontetrachloride to form a resin solution. The solution is mixed with a liquid where the resin separates from the mixture of the resin solution in the liquid and the resin is recovered. The liquid has a temperature higher than the boiling point of the solvent and has a specific gravity smaller than that of the solvent and larger than that of the resin. The liquid is preferably water.